1. Field of the Invention
The present invention relates in general to a device for detecting a rotating speed of a vehicle, and more particularly to a technique for improving the detecting accuracy of the device.
2. Discussion of the Prior Art
There is a need of sensing the rotating speed of a wheel of an automotive vehicle. For instance, the speed of the vehicle wheel is detected in controlling an anti-skid brake system of the vehicle. A typical example of such a speed-detecting device includes an axle hub, an annular rotor having a toothed portion with a multiplicity of circumferentially spaced-apart teeth, and a detector operable to detect the teeth of the rotor while the rotor is rotated. The axle hub has a shaft portion, and a flange portion which extends radially outwardly from one of opposite axial ends of the shaft portion. The shaft portion includes an intermediate section at which the axle hub is rotatably supported by a suitable stationary member of the vehicle via a bearing. The rotor is secured to the axle hub so that the rotor is rotated with the wheel secured to the axle hub. Conventionally, the rotor is secured at its one end to the flange portion of the axle hub, as disclosed in INSTRUCTION MANUAL for Mitsubishi new model car, "Galant Eterna .SIGMA." (No. 1038830, Oct., 1984, page 3-38).
In the case where the rotor is secured to the radially outwardly extending flange portion of the axle hub, the rotor is subject to deformation as a result of deformation of the flange portion due to a bending moment repeatedly applied thereto upon turning motions of the vehicle. Consequently, the roundness of the toothed portion of the rotor is deteriorated, causing its teeth to be displaced toward and away from the axis of rotation of the rotor. Thus, the conventional detecting arrangement suffers from deterioration of the detecting accuracy during use. Although the above problem can be solved by using a massive axle hub with a rigid flange portion, this solution results in increasing the weight of the axle hub, and consequently an undesirable increase in the non-suspended or unsprung weight of the vehicle, which in turn leads to deteroriated driving comfort of the vehicle.
The conventional arrangement has another drawback that the flange portion of the axle hub is exposed to the external space, and consequently the rotor attached to the flange portion is contaminated with iron particles, muds, and other matters, which may cause inaccurate detection and damage of the detector. Further, the conventional arrangement requires anti-rust treatment of the rotor, which results in raising the cost of manufacture of the detecting device.
Further, the conventional arrangement requires a cumbersome procedure to remove the rotor, since the rotor is secured to the inner surface of the flange portion of the axle hub on the inner side of the vehicle, while being interposed between the flange portion of the axle hub and the bearing. Namely, the removal of the rotor requires costly steps for dismounting the axle hub from the stationary member.